Stabilizer tool block wear pad assembly

ABSTRACT

The present invention is for a drill string stabiliser tool ( 18 ) used in borehole drilling. The tool includes a symmetrical body ( 20 ) with a plurality of external recesses ( 22 ). The recesses ( 22 ) have internal opposite surfaces ( 23 ) which converge inwardly from the outer surface of the body. A pad assembly ( 24 ) is disposed in each recess ( 22 ) and includes a wedge block ( 28 ) with converging radially inwardly opposite side surface ( 29 ) complementarily abutting said recess surfaces. Each wedge block ( 28 ) has a bolt ( 30 ) securing said wedge block ( 28 ) to said body ( 20 ) and is slightly larger dimensioned than the recess ( 22 ). The angles of the wedge blocks and the recesses are so chosen to effect an interference fit so that when the wedge block ( 28 ) is forced into the recess ( 22 ) by use of the bolt ( 30 ) it is held there by an interference fit.

The present invention relates to stabiliser tool and a wedge assemblyfor use in stabiliser tools that stabilise the operation of a drillstring in a borehole drilling through the earth's surface.

BACKGROUND OF THE INVENTION

In operation boreholes are initially drilled as vertical holes and maythen curve to an inclined or horizontal direction. Maintaining ofcomplete control is very important but very difficult to achieve. Aborehole drill may, for example, include three cutters or reamers, whichare circumferentially spaced from one another. When the drill bit isinclined to the original axis, the space between the cutters can causeerratic or irregular operation in negotiating a curve.

So as to maintain control of the drill string, it is known to use astabiliser tool having projecting wear pad assemblies. Generally astabiliser tool includes recesses containing projecting pad assembliesarranged in a spaced configuration, with each pad assembly generallyhaving two outer blocks and a central wedge block. The recesses have atleast two side walls that diverge radially inwardly by an included angleproviding an undercut recess surface. The outer blocks include divergingouter side walls of the same angle as the recess side walls. The outerwalls are retained in abutment with the undercut recess surface by thewedge block acting on the inner walls of the outer blocks, the centralwedge block having inwardly converging walls of the same angle as thediverging inner walls of the outer blocks. An appropriate bolt draws thecentral wedge into the gap between the outer blocks and causes them tomove outwardly into firm abutment with the undercut recess thus lockingthem in place. The advantage of this configuration is that to repair orreplace the wear pad assemblies one only needs to remove the centralwedge block between the two outer blocks that then can be moved towardseach other and away from the recess walls that locked them in place.

The difficulty with that configuration is that if the bolt locking thecentral wedge assembly in the recess were to break the central wedge maycome away from the recess. This then allows the outer blocks to moveaway from the recess side walls and away from the recess. The end resultis that the drill string may be jammed in a borehole, whereuponabandonment is unavoidable. In addition, not only is a multi-block wearpad assembly relatively expensive to manufacture, the manufacture of arecess with inwardly diverging side walls is also a complex task. Sincethe cost of the drill string is quite high it is an object of thepresent invention to provide improvements in stabiliser tools whichovercome at least some of the abovementioned problems or provide auseful alternative.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the invention a drill string stabiliser tool has a bodyhaving an outer surface symmetrical about an axis of rotation, and aplurality of recesses extending inwardly from said outer surface;

said recesses each including opposite surfaces which converge inwardlyfrom said body outer surface;

a plurality of pad assemblies in respective said recesses, each said padassembly including a wedge block with converging radially inwardlyopposite side surfaces complementary abutted by said recess surfaces;

each said wedge block having a relatively hard outer wear surfacelocated radially outwardly from said body surface, and a bolt securingsaid wedge block to said body;

characterised by the outer side surfaces of the wedge block converginginwardly at a pre-determined angle and the opposite surfaces of saidrecesses converging inwardly at the same pre-determined angle wherebysaid angle is so chosen to provide an interference fit between the outerside surfaces of said wedge block and opposite surfaces of saidrecesses.

It has been surprisingly found that, even under immense forces that maybe imposed on the wedge (wear) blocks and that are transmitted to theinwardly converging recess surfaces, the interference fit locks thewedge blocks in their recesses and resists the tendency of them to beremoved by compressive forces, turning moments, or both even if thecentral bolt locking the wedge were to break. This then allows the drillstring to be removed from the borehole and the pad assembly to berepaired without having to be abandoned.

This is an unexpected result for intuitively it is thought that a recesswhose sides are inwardly converging would need a locking mechanism, suchas a bolt to hold the wedge block in the recesses. It has previouslybeen assumed that an engaging member such as a bolt passing through theassembly locks the pad assemblies in place. Accordingly there have beena number of proposals for secondary locking mechanisms to prevent theloss of a drill string. It has however been the unexpected discovery bythe present inventor, that such an interference fit provides thenecessary locking force to keep the assembly locked in place and thatthe central bolt is essentially only required to urge the wedge blockinwardly and outwardly to achieve or break the interference fit.

To assist in achieving an interference fit, the total size (or width) ofthe wedge block is preferably slightly larger (wider) than that of therecess. This ensures that an interference fit is properly achieved whenthe wedge block is urged into the recess. Generally one would calculatethe width of the recess and the wedge block would then be manufacturedto be of slightly larger dimension than the dimensions of the recess. Inpreference it has been found that if the wedge block is {fraction(3/1000)} of an inch greater in width than the remaining width of therecess an effective interference fit occurs.

Thus to assemble the pad assembly a bolt is used to draw the centralwedge into the recess resulting in an interference fit locking theassembly in place. To remove the pad assembly it is also necessary forthe bolt to urge the wedge block outwardly and thus break theinterference fit. Accordingly in use even if the central bolt were tobreak the interference fit has been found to lock the assembly in place.

In preference the predetermined angle depends on the material from whichthe assembly is manufactured. If made from steel, an angle of some 2degrees has been found to produce an interference fit. However a rangeof angles of between 1.5 to 3.5 degrees has also been found to achievean interference fit if the angle is greater or smaller than that rangeit has been found that an interference fit is not achieved and the wedgeblock is then only held in place by the bolt. If this were to break in aborehole than this could lead to the pad assembly becoming loose andbeing jammed in the borehole. Preferably the angle is some 2 degrees.

Further in the invention, there may be provided hard tipped cutters (forexample polycrystallised diamond cutters) projecting outwardly from thesides of the wedge block, and if these are located towards the top endof the stabiliser and above the reamers of a drill string, the wall of asmall bore hole will be enlarged upon withdrawal, thereby reducinglikelihood of the drill string being jammed and lost in the hole. Anegative rake of the cutters will still provide a cutting action, butmay be effective in firmly compacting loose earth or rock uponwithdrawal and avoid exacerbating the resistance to withdrawal byunnecessarily adding loose material between the cutters and reamers.

Preferably the wear blocks are positioned in a helical or spiral patternthat ensures that the drill stem upwardly of the reamers remainscentralised, and during drilling, being above reamers (when used) theblocks will engage borehole surfaces which are more regular both in sizeand in smoothness than would exist if the reamers were not present. Thestiffness below the stabiliser body of a reamer body and the bitassembly does much to avoid the difficulties previously encountered dueto the spacing between the bits and the bit assembly, and thereby muchimproves the ability of an operator to control the direction of the bitmovement.

In preference said wedge blocks are generally rectilinear in elevation,and side edges thereof are parallel in a plane normal to an axis of saidbolt.

In preference each of some at least of said wedge blocks further includeprojecting hard tipped cutters.

In a further aspect of the invention there is proposed a drill stringstabiliser tool including;

a) a body having an outer surface symmetrical about an axis of rotation,and a plurality of recesses extending inwardly from said outer surfaceand spaced in a helical configuration, said recess surfaces includingopposite surfaces which converge inwardly from said body outer surface,each said recess being symmetrical about a central radial plane of saidbody;

b) a plurality of pad assemblies in respective said recesses, each saidpad assembly having a wedge block having at least one pair of oppositesides converging towards said axis of rotation;

c) each said wedge block having a relatively hard outer wear surfacelocated radially outwardly from said body surface, and a bolt securingsaid wedge block to said body;

e) each said wedge block containing surfaces defining a bolt holeextending from its said outer wear surface to a radially inner surface,slot surfaces extending transversely from a side of said wedge blockdefining a lateral slot extending across said bolt hole;

f) a U-shaped washer contained in said slot, and said bolt having a headbearing against said washer, accommodated in said slot, and accessiblethrough said bolt hole from a said outer wear surface of said wedgeblock; wherein

the at least one pair of opposite sides of the wedge block converginginwardly at a pre-determined angle and the opposite surfaces of saidrecesses converging inwardly at the same pre-determined angle wherebysaid angle is so chosen to provide an interference fit between the outerside surfaces of said wedge block and opposite surfaces of saidrecesses.

In preference at least some of said wedge blocks include projecting hardtipped cutters, said hard tipped cutters being arranged in an array withthe extent of projection of the cutters from a said block increasingfrom the trailing end of said block to the leading end thereof, withrespect to a boring direction of drill string rotation.

In preference it is only the uppermost of said wedge blocks that havesaid projecting hard tipped cutters.

In a yet further form of the invention there is proposed a drill stringstabiliser including;

a) an elongate body adapted for rotation about a body axis;

b) the body including an outer surface including a plurality of spacedperimetral recesses arranged in a helical array;

c) a plurality of wear pads each positioned in an associated one of therecesses;

d) each pad having spaced side surfaces each complemental with anassociated side surface of the associated recess;

e) the side surfaces of each associated pad and recess convergingoppositely from the body surface to a base of the recess at an obtuseangle whereby to provide retention of each such pad in its associatedrecess by an interference fit;

f) each pad including a wear surface for drill string guiding engagementwith a wall of a bore hole; and

g) the complemental surfaces being position transversely of imaginaryplanes bisecting the body whereby forces applied to the mechanisms dueto frictional engagement of the wear surfaces with a bore hole wall areapplied transversely of the complemental surfaces.

In a still further from of the invention there is proposed a wear padassembly for use with drill string stabiliser tools of the type having aplurality of recesses having inwardly converging side walls, said wearpad assembly including;

a wedge block having at least one pair of opposite side surfaces eachside surface so shaped to complementary abut said recess surface;

each said wedge block having a relatively hard outer wear surfacelocated radially outwardly from said body surface, and a bolt securingsaid wedge block to said body;

said outer side surfaces of the wedge block converging inwardly at apredetermined angle that is the same as the angle of the inwardlyconverging side walls of said recess, said angle being such so as toprovide an interference fit between the outer side surfaces of saidwedge block and the side walls of said recess.

Preferably said interference angle is between 1.5 to 3.5 degrees.Preferably the dimensions of the wedge block is slightly greater thanthat of the recess.

BRIEF DESCRIPTION OF THE DRAWINGS

Two embodiments of the invention are described hereunder in some detailwith reference to and as illustrated in the accompanying drawings, inwhich:

FIG. 1 is a fragmentary elevation which illustrates a reamer of a drillstring surmounted by a drill bit stabiliser tool, according to a firstembodiment;

FIG. 2 is a cross-section taken on line 2—2 of FIG. 1, drawn to a largerscale;

FIG. 3 is a schematic cross-sectional view of a pad assembly, showingthe relative dimensions of the blocks prior to assembly;

FIG. 4 is a schematic cross-sectional view of a pad assembly, after theblock has been assembled;

FIG. 5 is a front elevation of a pad assembly;

FIG. 6 is a perspective view of a pad assembly according to a secondembodiment;

FIG. 7 is a front view of the pad assembly of FIG. 6; and

FIG. 8 is a fragmentary section taken on line 6—6 of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the above figures it is to be understood that likeelements are described by like numerals in the drawings. There is thusshown a drill string 10 that is provided with a bit assembly (notshown), and that is surmounted by a roller reamer 12 having threerollers 14 each with hard inserts 16 which may project or be flush withthe outer surfaces of the rollers.

Above the roller reamer 12 there is provided the stabiliser tool 18 ofthis invention. Stabiliser tool 18 comprises a generally cylindricalbody 20 rotatable about axis A—A, and which has (in this embodiment)three helical rows of recesses 22 (FIG. 2), the side walls 23 ofrecesses 22 converging radially inwardly by an angle of between 1.5 to3.5 degrees. That angle is one that provide for an interference fit andprovides abutment surfaces for side walls of wear pad assemblies 24.

Each wear pad assembly 24 includes a wedge block 28 whose outer sidewalls 29 converge radially inwardly. The outer side walls 29 converge bythe same angle as the side walls 23 of the recesses 22. The central orwedge block 28 is urged inwardly and locked in place by a socket headbolt 30. The angle of the inwardly converging side walls 29 of thecentral wedge block is selected so as to provide an interference fit.

In the case of steel it has been found that angle may be some 1.5 to 3.5degrees. If the angle is less than this 1.5 degrees or greater than 3degrees it has been found that an interference fit does not occur andthe holding force is solely provided by the bolt. It is however to beunderstood that other angles may equally well provide an interferencefit, the angle being dependent on the material used.

The underside of the head of bolt 30 bears against a U-shaped washer 32which allows the bolt to be positioned in the central wedge block 28 andthe axially outer surface of the head of bolt 30 bears against anabutment surface 34, being an outer surface of a lateral slot 36 whichcontains washer 32 within the central block 28. There is an opening at38 to allow access for a key (not shown) to engage in a recess in thehead of bolt 30, both for tightening the wedge block 28 into positionand also for releasing the wedge block 28. The wedge block 28 isprovided with a hard metal surface 40, harder than the remainder of theblock.

As can be seen from FIG. 2, the walls of the recesses 22 in thisembodiment are symmetrical about a central radial plane marked AP inFIG. 2, although the outer hard surface 40 need not be symmetrical asdescribed below. The walls of the recesses are at converging angle tothe radial plane AP that results in an interference fit created betweenthe wedge and the recess surfaces.

To achieve an interference fit, it is preferable that the width of thewedge has to be slightly greater than that of the recess within which itis to be positioned. Thus, as seen in FIG. 3 the recess has a width 42(x). The central wedge block 28 is of a width 44 (x+y) that is slightlygreater than the width 42. The central block is then inserted into therecess, bolt 30 can then engage threaded bore 46 in the drill string 10and urge the central wedge into the recess gap until the bottom of thewedge abuts the bottom of the recess, and wherein the wedge block stillprotrudes form the recess beyond the outer surface of the body toprovide for the wear surface. Because the central wedge is slightlylarger than the gap into which it was urged, an interference fit isachieved.

FIG. 5 shows the wedge block 28 as seen when looking along the line fromP to A as shown in FIG. 2 which is central with respect to the socket,head bolt 30, and the side edges 52 of the. As shown in FIG. 5, viewedin the elevation the pad assembly 24 is approximately rectilinear(except for its corners) but as seen in FIG. 1, in other views it isnot.

When assembled, the bolt 30 bearing against the washer 32, urges thewedge block radially inwardly, since the washer 32 abuts the innersurface 54 of the slot 36, so that rotation of the socket head bolt 30in one direction will cause the wedge block 28 radially inwardly, but inthe opposite direction the head of bolt 30 will abut the surface 34 andwithdraw the wedge block. Once the wedge block is withdrawn, the bolt 30along with its U-shaped washer 32 can be moved outwardly away from thewedge block through the lateral slot 36.

Reference is now made to the second embodiment illustrated in FIGS. 6, 7and 8. In that embodiment, a wear pad assembly 56 includes a wedge block64 which is very similar to the wedge block 28 of the first embodiment.The bolt and washer arrangement is the same and those components bearthe same designations 30 and 32, as in the first embodiment. However, asillustrated, the hard surfaces 40 of the wedge blocks diminish in radiusfrom axis of rotation A towards the leading end 66 of a wedge blockrotation in respect of the boring direction of the drill string. Thusthere is provided a surface for tamping or compacting loose soilrearwardly of the leading end 66.

However, there is provided a plurality of tipped cutters 68, the tips 70of which comprise discs of polycrystalline diamond. The leading cuttersin respect of the boring direction of drill string rotation projectfurther outwardly than the trailing cutters, but the faces of the tips70 are inclined to provide a negative rake, which provides the mostuseful compromise in the cutters at that location. There are, however,only three pad assemblies with the tips as shown in FIGS. 6, 7 and 8,and those are the top three cutters of the stabiliser tool, the lowersix pad assemblies being as described with respect to the first andsecond embodiments. This combination of pad assemblies wherein the threeassemblies furthest from the reamers of the drill cutters provides ameans whereby the cutters on the pas assemblies can assist in thewithdrawal of a drill string, particularly when it is associated with acurved drill hole. In addition, this also provides means where, if thedrill is used in soft earth, there is to some extent some tamping andconsolidation of earth released by the cutters on the pad assemblies.This reduces to some extent the degree of build up of earth between thebody of the tool of this invention and a reamer assembly, therebyassisting to some extent in reducing the load applied to the drillstring. Furthermore, the cutters on the pas assemblies remain effectiveeven when rotation is reversed as can sometimes occur during withdrawalto facilitate removal of the drill string.

While the invention has been described in terms of several preferredembodiments, the person skilled in the art will appreciate the variousmodifications, changes and substitutions which may be made withoutdeparting from the scope of the invention. The descriptions of thesubject matter in this disclosure are illustrative of the invention andare not intended to be construed as limitations upon the scope of theinvention.

What is claimed is:
 1. A drill string stabilizer tool including a bodyhaving an outer surface symmetrical about an axis of rotation, and aplurality of recesses extending inwardly from said outer surface; saidrecesses each including opposite recess surfaces which converge radiallyinwardly from said body outer surface toward the axis of rotation; aplurality of pad assemblies in respective said recesses, each said padassembly including a wedge block with opposed outer side surfacesconverging radially inwardly toward the axis of rotation which arecomplementarily abutted by said recess surfaces; each said wedge blockhaving a relatively hard outer wear surface located radially outwardlyfrom said body outer surface, and a bolt securing said wedge block tosaid body; characterized by the inwardly converging outer side surfacesof the wedge block converging at a predetermined angle and the inwardlyconverging opposite surfaces of said recesses complementarily at thesame pre-determined angle whereby said angle is chosen to provide aninterference fit between the contacting complementarily outer sidesurfaces of said wedge block and opposite surfaces of said recesses asthe wedge block is drawn into the recess by said bolt to lock the wedgeblock in said recess.
 2. A drill string stabilizer tool including; a) abody having an outer surface symmetrical about an axis of rotation, anda plurality of recesses extending inwardly from said outer surface andspaced in a helical configuration, said recess surfaces includingopposite surfaces which converge inwardly towards the axis of rotationfrom said body outer surface, each said recess being symmetrical about acentral radial plane of said body; b) a plurality of pad assemblies inrespective said recesses, each said pad assembly having a wedge blockhaving an outer body surface and at least one pair of opposite sidesconverging towards said axis of rotation; c) each said wedge blockhaving a relatively hard outer wear surface located radially outwardlyfrom said outer body surface, and a bolt securing said wedge block tosaid body; e) each said wedge block containing surfaces defining a bolthole extending from its said outer body surface to a radially innersurface, slot surfaces extending transversely from a side of said wedgeblock defining a lateral slot extending across said bolt hole; f) aU-shaped washer contained in said slot, and said bolt having a headbearing against said washer, accommodated in said slot, and accessiblethrough said bolt hole from a said outer wear surface of said wedgeblock; wherein the inwardly converging at least one pair of oppositesides of the wedge block converge at a pre-determined angle and theinwardly converging opposite surfaces of said recesses complementarilyconverge at the same pre-determined angle whereby said pre-determinedangle is chosen to provide an interference fit between the contactingcomplementary outer side surfaces of said wedge block and oppositesurfaces of said recesses as the wedge block is drawn into the recess bysaid bolt to lock the wedge block in said recess.
 3. A drill stringstabilizer tool including; a) an elongate body adapted for rotationabout a body axis; b) the body including an outer surface including aplurality of spaced perimetral recesses arranged in a helical array; c)a plurality of wear pads each having wear surfaces and each positionedin an associated one of the recesses; d) each pad having spaced sidesurfaces each which are complementary to an associated side surface ofthe associated recess and having a bolt securing each pad to theassociated recess; e) the side surfaces of each associated pad andrecess complementarily contacting each other and converging oppositelyfrom the body surface to a base of the recess at a predetermined obtuseangle whereby to provide retention of each such pad in its associatedrecess by an interference fit between the contacting complementary sidesurfaces of each associated pad and recess as the associated pad isdrawn into the recess by said bolt so as to lock the pad in therecesses; f) each pad including a wear surface for drill string guidingengagement with a wall of a bore hole; and g) the complementary surfacesbeing position transversely of imaginary planes bisecting the bodywhereby forces applied to each element of the drill string stabilizertool due to frictional engagement of the wear surfaces with a bore holewall are applied transversely of the complementary surfaces.
 4. A drillstring stabilizer tool as in any one of the above claims wherein saidpre-determined angle is in the range between 1.5 to 3.5 degrees.
 5. Adrill string stabilizer tool as in claim 4, wherein the wedge blocks andthe recesses are manufactured from mild steel.
 6. A drill stringstabilizer tool as in claim 5 wherein said pre-determined angle isapproximately 2 degrees.
 7. A drill string stabilizer tool as in any oneof claims 1-3, wherein the wear blocks are positioned in a helicalcircumferentially disposed about the tool.
 8. A drill string stabilizertool as in any one of claims 1-3, wherein said wedge blocks aregenerally rectilinear in elevation, and side edges thereof are parallelin a plane normal to an axis of said bolt.
 9. A drill string stabilizertool as in any one of claims 1-3, further including hard tipped cuttersprojecting outwardly from the sides of the wedge block.
 10. A drillstring stabilizer tool as in any one of claims 1-3, wherein at least oneof said wedge blocks further includes projecting hard tipped cutters.11. A drill string stabilizer tool as in claim 10, wherein said hardtipped cutters are arranged in an array and such that the extent ofprojection of the cutters from a said block increases from the trailingend of said block to the leading end thereof, with respect to a boringdirection of drill string rotation.
 12. A drill string stabilizer toolas in claim 10, wherein it is only the uppermost of said wedge blocksthat have said projecting hard tipped cutters.
 13. A wear pad assemblyfor use with a drill string stabilizer tool of the type having aplurality of recesses each having side walls inwardly converging towardthe axis of rotation of the drill string, said wear pad assemblyincluding; a wedge block having a body surface and at least one pair ofopposite outer side surfaces such that each side surface is so shaped tocomplementarily abut said side walls of a recess; each said wedge blockhaving a relatively hard outer wear surface located radially outwardlyfrom said body surface, and a bolt securing said wedge block to saiddrill string stabilizer tool; said outer side surfaces of the wedgeblock converging inwardly at a pre-determined angle that is the same asthe angle of the inwardly converging side walls of said recess, saidpre-determined angle being such so as to provide an interference fitbetween the outer side surfaces of said wedge block and the side wallsof said recess as the wedge block is drawn into the recess by said boltto lock the wedge block in said recess.
 14. A wear pad assembly as inclaim 13, wherein said interference angels is in the range between 1.5to 3.5 degrees.
 15. A wear pad assembly as in claim 13, where thedimensions of each wedge block is slightly greater than that of therecess.